1. Field of the Invention
The present invention relates to an image receiving sheet for use in a thermal image transfer recording system, and more particularly to an image receiving sheet capable of receiving images from a thermal image transfer recording medium which can be repeatedly used for thermal printing.
2. Discussion of Background
Recording apparatus, such as a printer and a facsimile apparatus, using the thermal image transfer recording method, is now widespread. This is because the recording apparatus of this type is relatively small in size and can be produced inexpensively, and the maintenance is simple.
In the conventional thermal image transfer recording medium for use with the thermal image transfer recording apparatus, a single ink layer is merely formed on a support. When such a recording medium is used for printing images, the portions of the ink layer heated by a thermal head are completely transferred to an image receiving sheet at only one-time printing. Therefore, the recording medium can be used only once, and can never be used repeatedly. The conventional recording medium is thus disadvantageous from the economical point of view.
In order to overcome the above drawback in the prior art, there have been proposed the following methods:
(1) A microporous ink layer is formed on a support so that a thermofusible ink impregnated in the ink layer can gradually ooze out as disclosed in Japanese Laid-Open Patent Applications 54-68253 and 55-105579; PA1 (2) A porous film is provided on an ink layer formed on a support so that the amount of an ink which oozes out from the ink layer can be controlled as disclosed in Japanese Laid-Open Patent Application 58-212993; and PA1 (3) An adhesive layer is interposed between an ink layer and a support so that an ink of the ink layer can be gradually exfoliated in the form of a thin ink layer from the support when images are printed as disclosed in Japanese Laid-Open Patent Applications 60-127191 and 60-127192.
However, when images are printed on an image receiving sheet in general use by using the above-mentioned thermal image transfer recording media, the image density of the obtained images is lowered or changed during the repeated printing operation.
Many proposals have also been made to eliminate the above drawback from the image receiving sheet for use in the thermal image transfer recording system.
For instance, image receiving sheets comprising a support and a coating layer with a high oil-absorbability are disclosed in Japanese Laid-Open Patent Applications 57-182487, 61-217289, 61-248791, 61-266296, 61-284486, 62-162590, 62-202788, 62-160287, 62-257888, 62-278082, 63-19289, 63-69685, 63-178082 and 01-188392.
However, even when the aforementioned image receiving sheets with a high oil-absorbability are used for thermal image transfer recording, the obtained images lack high resolution, and high image density cannot be maintained during the repeated printing operation.
Japanese Laid-Open Patent Application 02-9688 discloses that satisfactory images can be obtained when an image receiving sheet with a surface roughness index (Vr) of 5 ml or more in accordance with the Bristow's method (J.TAPPI Testing Method for Paper and Pulp No. 51-87). When the thermal image transfer recording medium is repeatedly used for printing images on such an image receiving sheet, however, images with high resolution and high density cannot be maintained for an extended period of time.